I can't speak for the neighbour of this semi-detached property, I don't know if they objected to this application or indeed happily approve of it, but from a personal point of view I think that a level of symmetry needs to be maintained and I would have fought this tooth and nail.
Call me the neighbour from hell but when my new (fortunately detached) neighbour purchased the property next door to me and immediately put in an application to demolish it, I took it all the way through four planning applications until the proposed development had been compromised as much as possible.
Why? Because I simply wasn't prepared to have my house and garden which I had worked damn hard to buy, overlooked, overshadowed and blighted by a property which was also three times the size of the original.
One of the biggest problems with many planning applicants is there total lack of consideration for their neighbours. Worse still, having got approval and had it built, they often then immediately sell it and move on.
Regardless of whether the neighbour has objected or approved of this, unless they move out while this is being built, they are surely going to be put through hell.